1. Field
A rotary compressor, a method of manufacturing a rotary compressor, and an apparatus for manufacturing a rotary compressor are disclosed herein.
2. Background
In general, compressors may be mechanical devices that receive power from power generation devices, such as an electric motor or a turbine, to compress air, a refrigerant, or an other working gas, thereby increasing a pressure of the air, refrigerant, or working gas. Compressors are being widely used in home appliances, such as refrigerators and air-conditioners, or whole industrial machinery fields.
Compressors may be largely classified as a reciprocating compressor, in which a compression space into and from which a working gas is suctioned and discharged, is defined between a piston and a cylinder to compress the working gas while the piston is linearly reciprocated within the cylinder; a rotary compressor, in which a compression space into and from which a working gas is suctioned and discharged, is defined between a roller which is eccentrically rotated and a cylinder to compress the working fluid while the roller is eccentrically rotated along an inner wall of the cylinder; and a scroll compressor, in which a compression space into and from which a working gas is suctioned or discharged, is defined between an orbiting scroll and a fixed scroll to compress the working fluid while the orbiting scroll is rotated along the fixed scroll.
FIGS. 1 to 4 are schematic diagrams of a rotary compressor according to a related art. Referring to FIG. 1, the rotary compressor according to the related art may include a case 1a that defines an inner space, and a top cover 1b coupled to an upper portion of the case 1a. A stator 2 that generates a magnetic force using a power source applied thereto, and a compression mechanism 3 that compresses a refrigerant using an induced electromotive force generated by interaction with the stator 2 may be disposed in the case 1a. 
The compression mechanism 3 may include a rotor 3a rotatably disposed inside of the stator 2. The stator 2 and the rotor 3a may be understood as components of a compressor motor. Also, the compression mechanism 3 may further include a rotational shaft 4 coupled to the rotor 3a to rotate according to rotation of the rotor 3a. 
The rotary compressor may further include a roller 5 eccentrically coupled to a lower portion of the rotational shaft 4 to rotate with a predetermined eccentric trace according to the rotation of the rotational shaft 4, a cylinder 6, in which the roller 5 may be accommodated, and main and sub bearings 7 and 8, respectively, disposed on upper and lower portions of the cylinder 6 to support the cylinder 6. Each of the main and sub bearings 7 and 8 may have an approximately disc shape to support each of the upper and lower portions of the cylinder 6.
The rotary compressor may further include a vane (not shown) that reciprocates within a slot defined in the cylinder 6 according to the rotation of the roller 5 to separate a suction chamber from a compression chamber, a suction hole 9 and a discharge hole, each of which may define a flow path of the refrigerant that is suctioned into and discharged from the cylinder 6, and a muffler 11 disposed on or at an upper portion of the discharge hole to reduce discharge noise of the refrigerant.
An operation according to the above-described components will be described hereinbelow. When the rotational shaft 4 rotates, the roller 5 may rotate and revolve along an inner circumferential surface of the cylinder 6 while drawing a predetermined eccentric trace. The refrigerant may be introduced into the suction chamber of the cylinder 6 through the suction hole 9. The refrigerant may be compressed in the compression chamber while the roller 5 rotates.
When the compression chamber has an inner pressure higher than a discharge pressure, a discharge valve (not shown) disposed at one side of the discharge hole may be opened, and then the compressed refrigerant may be discharged from the discharge hole through the opened discharge valve. The discharge valve may be disposed in the main bearing 7 disposed on the upper portion of the cylinder 6. The refrigerant discharged through the discharge hole may be introduced into the muffler 11 disposed on an upper portion of the main bearing 7. The muffler 11 may reduce the noise of the discharged refrigerant.
The main bearing 7 may be disposed on the upper portion of the cylinder 6 to disperse a compression force of the refrigerant generated in the cylinder 6 or a force (hereinafter, referred to as a “motor force”) generated by the stator 2 and the compression mechanism 3 toward the case 1a. Referring to FIGS. 2 and 3, the main bearing 7 may include a plurality of coupling parts or portions W1 coupled to the case 1a. Each of the plurality of coupling portions W1 may be understood as a “welding” provided by welding the main bearing 7 to the case 1a. The main bearing 7 may have almost a same diameter as or a diameter slightly less than an inner diameter of the case 1a so that the main bearing 7 may be coupled to the case 1a through the plurality of coupling portions W1.
On the other hand, the sub bearing 8 may be disposed at the lower portion of the cylinder 6 to support the cylinder 6. The sub bearing 8 may have a diameter less than the inner diameter of the case 1a. The sub bearing 8 may have an outer circumferential surface that is spaced apart inward from the case 1a. 
That is, in the rotary compressor according to the related art, as the main bearing 7 has to be coupled to the case 1a by welding, the case 1a needs to have a predetermined hole for the welding. Thus, the assembling process of the compressor is complicated.
Also, when the welding is defective, the refrigerant may leak, and an imbalance in power between the plurality of coupling portions, that is, weldings, W1 may occur, generating a rotational moment at the cylinder 6 and the main bearing 7 in a predetermined direction. Also, as a predetermined air gap defined between the stator 2 and the rotor 3a may be non-uniform, that is, increase or decrease due to the rotational moment, noise from the stator 2 and the compression mechanism 3 may increase. That is, as illustrated in FIG. 4, the air gap g1 may be non-uniform between an inner circumferential surface l1 of the stator 2 and an outer circumferential surface l2 of the rotor 3a generating noise.